A marine organism, for example, a barnacle, an oyster, a blue mussel, a hydra, a serpula, a sea squirt, a moss animal, a sea lettuce, a green layer or an attached diatom adheres to a portion of an underwater structure, for example, a ship in contact with seawater to proliferate, thereby causing an unfavorable state, for example, a reduction in facility mechanical performance, e.g., an increase in fluid resistance or a reduction in thermal conductivity, or diffusion of the adhering marine organism to overseas. In addition, an operation of removing the adhering marine organism requires a great deal of labor and an enormous amount of time, which results in economic loss.
In order to prevent the damage as described above, hitherto, the underwater structure is painted with an antifouling paint. The antifouling paint contains a toxic antifouling agent, which, for example, was formerly an organotin compound and is currently cuprous oxide. Although adhesion and growth of the marine organism can be suppressed almost completely by the toxicity of the antifouling paint, the toxic antifouling agent, for example, the organotin compound or cuprous oxide causes a serious problem in the long run because the agent adversely affects a human body or an environment to no small extent. In addition, when the antifouling paint is dried after its painting, about 30% by weight of an organic solvent (VOC) volatilizes to adversely affect a work environment or a surrounding environment. In spray-type painting, in addition to discharge of the VOC to the atmosphere, from 10% to 20% by weight of the paint is said to be scattered to the surroundings by the wind. On the other hand, when the structure painted with the antifouling paint that has been used for many years is repainted with a new one, the antifouling paint that has become old is peeled with a sandblast or a metal grinder. At that time, however, a large amount of coating film pieces each containing the toxic antifouling agent, for example, the organotin compound or cuprous oxide are scattered to the surroundings to adversely affect an operator or the environment. In addition, the antifouling paint peeled is treated as industrial waste. Accordingly, the paint has been causing a major problem.
As described above, the conventional antifouling paint has an inhibiting effect on the adhesion of marine organisms, but adversely affects the human body or the environment to a large extent, which still has many unsolved problems to the present date.
Accordingly, there has been proposed a pressure-sensitive adhesive tape formed by bonding a copper foil and a pressure-sensitive adhesive to each other through a primer (see Patent Documents 1 and 2). However, since the suppression of the adhesion of marine organisms in the pressure-sensitive adhesive tape is attained by a copper component in the copper foil, there is a problem in that the tape may adversely affect the environment. In addition, the peel adhesive strength for an FRP plate of the pressure-sensitive adhesive tape is designed to be extremely large, specifically, 2.6 kg/25 mm or 7.5 kg/25 mm (after primer pretreatment). Thus, it is difficult to consider that the pressure-sensitive adhesive tape after use can be easily peeled by human power when the pressure-sensitive adhesive tape is replaced with another tape. Ultimately, a great deal of labor is needed because an action, for example, scraping is needed. In addition, since copper has a specific weight of 8.94 g/cm3, which is a heavy substance, the use of copper for a movable structure, for example, a ship deteriorates fuel efficiency and is not preferred from an economic viewpoint.
In addition, there has been proposed an antifouling tape composed of two layers, i.e., a silicone rubber layer and a pressure-sensitive adhesive layer (see Patent Document 3). However, the silicone rubber layer responsible for an antifouling effect does not contain an antifouling agent, for example, an oil, and hence is the silicone rubber itself. In the case where the antifouling agent is not contained, the adhesion of marine organisms can be suppressed by the water-repellent property of the silicone rubber for a short period of time, but the antifouling effect is not sustained for a long period of time. In addition, extreme concern is raised about the strength of the antifouling tape because the tape is composed of two layers, i.e., a silicone rubber and a pressure-sensitive adhesive. In general, the silicone rubber has an extremely low strength at break and thus, the case where the antifouling tape is peeled after use is not realistic because it is difficult to peel the tape while maintaining its tape form.
Therefore, in order to increase the strength, it is conceivable to provide a base material layer.
For example, there has been proposed a sheet-shaped tape including a silicone elastomer provided on a base material layer through an undercoating agent and a pressure-sensitive adhesive layer provided on the opposite side of the base material layer (see Patent Document 4). The sheet-shaped tape disclosed in Patent Document 4 contains a fluorine-containing liquid compound and/or a hydrophobic silicone-based liquid compound as an antifouling agent. However, the sheet-shaped tape containing the antifouling agent cannot express sufficient antifouling performance. In addition, in Patent Document 4, since there is no description at all about the composition of a pressure-sensitive adhesive usable in water or about the adhesive strength of the tape, the application of the tape to a pressure-sensitive adhesive tape for preventing adhesion of aquatic organisms lacks reality. In addition, in the application of an antifouling tape to an underwater structure, the flexibility and elongation property of the tape need to be designed such that the tape can be applied to a curved surface or an acute angle surface. In addition, the strength of the tape needs to be designed such that the base material layer is prevented from breaking during the peeling of the antifouling tape after use. However, in Patent Document 4, since there is no description at all about these properties, the application of the tape to a pressure-sensitive adhesive tape for preventing adhesion of aquatic organisms lacks reality.
In the case of considering a base material layer as a component of the pressure-sensitive adhesive tape for preventing adhesion of aquatic organisms, cost reduction of the base material itself is one of the big issues. As a material for inexpensive base material (approximately 100 yen/m2 or less), vinyl chloride, polyethylene or the like is exemplified. However, when a conventional silicone-based antifouling layer is provided on a base material layer composed of such a material, since a problem in that the antifouling layer is peeled off from the base material layer arises, it is necessary to increase adhesion between the base material layer and the antifouling layer.
As a technical means for improving the adhesion between the base material layer and the antifouling layer, an easy adhesion treatment, for example, a primer treatment or a corona treatment to a surface of the base material layer is exemplified. However, when the easy adhesion treatment is performed, there is a problem in that the manufacturing process of the pressure-sensitive adhesive tape for preventing adhesion of aquatic organisms increases.